System and method of assessing analgesic adequacy using biopotential variability

Abstract

The system and method for predicting and measuring a subject's analgesic state and analgesic adequacy. Biopotential signals are obtained from a subject through electrodes. A processor will compute a measure that is representative of the subject's sedative state and/or muscle activity. A metric representative of such measures is then determined. In the case where a measure is taken of both the subject's sedative state and muscle activity the two measures are combined into an index representative of the subject's analgesic state and analgesic adequacy.

What is claimed is: 
     
         1 . A method for assessing a subject's analgesic state and adequacy comprising:
 obtaining biopotential signals from the subject at intervals over a period of time using a plurality of electrodes;   computing from the biopotential signals a first measure representative of the subject's sedative state;   calculating a first metric representative of variability of the first measure;   computing from the biopotential signals a second measure representative of the subject's muscle activity;   calculating a second metric representative of variability of the second measure; and   calculating from the first and second metrics an index representative of the subject's analgesic state and analgesic adequacy.   
     
     
         2 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , further comprising:
 assigning weights to at least one of the first and second metrics, and   calculating an index from at least one of the first and second metrics based on the weights.   
     
     
         3 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , wherein calculating the index comprises combining the first metric and the second metric to calculate the index representative of the subject's analgesic state and analgesic adequacy. 
     
     
         4 . The method for assessing a subject's analgesic state and adequacy of  claim 3 , further comprising:
 assigning weights to the first metric and the second metric, and   combining the first metric and the second metric into the index based on the weights.   
     
     
         5 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , further comprising time synchronizing the first measure and the second measure. 
     
     
         6 . The method for assessing a subject's analgesic state and adequacy of  claim 3 , wherein combining the first and second metrics includes combining the first and second metrics in a linear combination. 
     
     
         7 . The method for assessing a subject's analgesic state and adequacy of  claim 6 , wherein the linear combination is a logistic equation. 
     
     
         8 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , wherein the first metric representative of variability is based, at least in part, on standard deviation of the first measure, and the second metric representative of variability is based, at least in part, on standard deviation of the second measure. 
     
     
         9 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , further comprising smoothing the index by averaging a plurality of index values. 
     
     
         10 . The method for assessing a subject's analgesic state and adequacy of  claim 1  further comprising displaying the index representative of the subject's analgesic state and analgesic adequacy. 
     
     
         11 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , further comprising calculating a first alternate index representative of the subject's analgesic state and analgesic adequacy from the first metric representative of variability. 
     
     
         12 . The method for assessing a subject's analgesic state and adequacy of  claim 11 , further comprising calculating a second alternate index representative of the subject's analgesic state and analgesic adequacy from the second metric representative of variability. 
     
     
         13 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , wherein the first metric representative of variability is based, at least in part, on a first confidence interval associated with the first measure, and the second metric representative of variability is based, at least in part, on a second confidence interval associated with the second measure. 
     
     
         14 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , wherein the first metric representative of variability is based, at least in part, on a first threshold associated with the first measure, and the second metric representative of variability is based, at least in part, on a second threshold associated with the second measure. 
     
     
         15 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , wherein the first metric representative of variability is based, at least in part, on a first standard error associated with the first measure, and the second metric representative of variability is based, at least in part, on a second standard error associated with the second measure. 
     
     
         16 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , wherein the first metric representative of variability is based, at least in part, on a first range associated with the first measure, and the second metric representative of variability is based, at least in part, on a second range associated with the second measure. 
     
     
         17 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , wherein the intervals over a period of time comprise 15 second intervals. 
     
     
         18 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , further comprising smoothing the index by assigning weights to each of a plurality of index values and by averaging the plurality of index values based at least in part on the weights. 
     
     
         19 . The method for assessing a subject's analgesic state and adequacy of  claim 1 , wherein calculating from the first and second measures an index comprises determining from which of the first and second measures to calculate the index. 
     
     
         20 . The method for assessing a subject's analgesic state and adequacy of  claim 19 , further comprising determining from which of the first and second measures to calculate the index based on the subject's EEG state.